This commit adds two related changes:
* ILM WaitForDataTierStep
* Autoscaling frozen_existence decider
The first part ensures that we wait mounting an index until a node that
can hold the index is available, avoiding a failed restore and red
cluster state. This is in particular important for the frozen phase, but
is done generically in the searchable snapshot action.
The second part triggers on indices in the ILM frozen phase to scale the
tier into existence by requiring a minimal amount of memory and storage.
Closes#72771
77938381ea